It may sound counterintuitive, but the last thing you want is to be reasonable or understanding right now. He needs to fully understand how much he has to lose with this behavior.
He will be in NY for a week then when he returns he would need to go into quarantine till the end of the month. So we will not be seeing him for a month and I need to hold off confronting him till he is back home.
This, in the quote box above, sounds like he isn't aware that you've found out about the OW. Is that correct? If so, there's one of two ways I'd go about addressing this. If I didn't want him back and I wanted a favorable divorce, I'd hire a PI and get evidence of the adultery to use in court. I'd also line up an attorney and have him served when he got off the plane. OTOH, if I did want a chance to reconcile the marriage, I'd call him on the phone and I'd keep calling and texting until he picked up. Then, I'd tell him that I know where he is and I know who he's with and that if he's not on the next flight out coming home(know when that is), he can just stay there. Don't be nice about it. Don't get bogged down in any discussion. Just put it out there, hang up, and let his imagination do the rest. Remember, that in his imagination, you're changing your Facebook status to "Married to a Disgusting Cheater" and you're ripping up his shirts before throwing them out on the lawn to burn in the car fire you made out of his ride.
You've been married 18 years. You'll be getting half of everything, including any retirement he's put away. He'll be losing the respect of his child, his extended family, friends, and social circle. He's got A LOT to lose. Most of the time, the cheater isn't looking to change his circumstances. He's just looking for MORE, and he doesn't believe he'll be caught. Once he knows he's caught, he'll start doing the math. And don't think that it's just about the stuff. It's not. We are part of that calculation, and many cheaters don't really know how they feel about the spouse they've betrayed until they're actually confronted with the prospective loss of that spouse. IOW, they've filled up their heads with a bunch of bullshit fantasies and they don't know what they don't know until the incursion of REALITY.
Anyway, don't be afraid to throw a full-on tantrum. What have you got to lose that's literally not already gone??? Refrain from abuse, of course, but let him have it with both proverbial barrels. Your reaction should command RESPECT. He lied to you. This wasn't about "depression" or "needing to travel". This was about adultery, so you call him out on that.
I had been married over 30 years before I caught my WH on a Craigslist binge which lasted the better part of a year. There were multiple partners and various levels of emotional attachment. On the day I confronted him, I told him I was getting a divorce and that I didn't care to hear any of his excuses or any of any details. I walked away and started doing "The 180" before I even knew what it was. (You can find more information on that in the Healing Library, btw.)
It was probably about a week before he screwed up his courage to approach me and ask for more time, thirty days to prove he could be trusted. I was like, "okay, it's been thirty years, I can wait thirty days". Sure enough though, I busted him in contact with one of the OWs. At that point it was a very stark choice. He could be "all in" or "all out", and not later, but right now. I gave him about thirty seconds to decide before I decided for him. He chose to ghost the OW and that was over six years ago. We're still together and mostly content, although I'd be lying if I said I still love him the way I once did. But that's a story for another day, right? For the moment, I think it would be a really GOOD thing for you to impress upon your WH that you are NOT an "option". At the moment, having his respect has a good deal more utility than having his dubious "love", right?
Remember that no matter how this situation plays out, you're going to be okay. It doesn't feel that way, I know. But we're all living proof that it gets better.